The vote was 69-29, including 15 Republicans who voted in favor of the amendment.

The Senate then agreed to invoke cloture on the Committee Substitute Amendment to the immigration bill with a vote of 67-31. Supporters of the immigration plan still hope to pass the full bill by week's end.

The border security amendment doubles border patrol agents to 40,000 officers and calls for the construction of 700 miles of fencing along the U.S.-Mexico border before 11 million undocumented immigrants can apply for citizenship. In all, the plan devotes a total of $30 billion to border security.

Hoeven took to the floor shortly before the vote, saying "Americans want immigration reform, but they want border security first and that's exactly what this amendment does."

On the opposing side, Sen. Chuck Grassley, R-Iowa, said the amendment wasted money by not including proper accountability measures in the plan.

"It throws money at the border, but there's no accountability to getting the job done," Grassley said. "This amendment is the wrong answer."